1. Technical Field
The present disclosure relates to a positive electrode material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
2. Related Art
In recent years, a polyanion-based positive electrode active material typified by lithium iron phosphate (LiFePO4) has been studied as a positive electrode active material having excellent crystal stability and thermal stability even at high temperatures. For instance, a nonaqueous electrolyte battery containing LiFePO4 as a positive electrode active material has already been put into practical use in electric tools. This battery has a high discharge capacity of approximately 160 mAh/g. This battery also has excellent high-rate performance due to a technique for allowing the surface of a positive electrode active material to carry an electronically conductive carbonaceous material.
However, the operating potential of LiFePO4 is 3.42 V relative to Li/Li+ reference, and is lower than the operating potential of a positive electrode active material used for a general battery. Therefore, LiFePO4 is insufficient in terms of energy density and output characteristic.
In view of this, Li3V2(PO4)3 has been suggested as the polyanion positive electrode active material which has higher operating potential than LiFePO4.
It is known that a nonaqueous electrolyte battery containing Li3V2(PO4)3 as a positive electrode active material exhibits a capacity as high as 130 mAh/g at low-rate discharge (see, for example, JP-T-2001-500665 and JP-T-2002-530835).